The present invention pertains to multi-circuit electronic communication systems, and more particularly, to a dedicated transmission channel structure for use in such systems.
Various means of electronic transmission are known in the art. Most, if not all of these transmission means, suffer from inherent speed limitations such as both the upper frequency limit and the actual time a signal requires to move from one point to another within the system, which is commonly referred to as propagation delay. They simply are limited in their electronic performance primarily by their structure, and secondarily by their material composition. One traditional approach utilizes conductive pins, such as those found in an edge card connector as is illustrated in FIG. 1. In this type of structure a plurality of conductive pins, or terminals 20, are arranged within a plastic housing 21 and this arrangement provides operational speeds of about 800 to 900 MHz. An improvement upon this standard structure is represented by edge card connectors that may be known in the art as “Hi-Spec” and which are illustrated in FIG. 2, in which the system includes large ground contacts 25 and small signal contacts 26 disposed within an insulative connector housing 27. The smaller signal contacts 26 couple to the larger ground contacts 25. The signal contacts in these structures are not differential signal contacts, but are merely single-ended signal, meaning that every signal contact is flanked by a ground contact. The operational speeds for this type of system are believed to be about 2.3 Ghz.
Yet another improvement in this field is referred to as a “triad” or “triple” connector in which conductive terminals are disposed within a plastic housing 28 in a triangular pattern, and the terminals include a large ground terminal 29, and two smaller differential signal terminals 30, as illustrated in FIG. 3, and, as described in greater detail U.S. Pat. No. 6,280,209. This triad/triple structure has an apparent upper limit speed of about 4 Ghz. All three of these approaches utilize, in the simplest sense, conductive pins in a plastic housing in order to provide a transmission line for electronic signals.
In each of these type constructions, it is desired to maintain a dedicated transmission line through the entire delivery path of the system, including through the circuit board(s), the mating interface and the source and load of the system. It is difficult to achieve the desired uniformity within the system when the transmission system is constructed from individual pins. Discrete point-to-point connections are used in these connectors for signal, ground and power. Each of these conductors was designed as either a conductor or a means of providing electrical continuity and usually did not take into account transmission line effects. Most of the conductors were designed as a standard pinfield so that all the pins, or terminals, were identical, regardless of their designated electrical function and the pins were further arranged at a standard pitch, material type and length. Although satisfactory in performance at low operating speeds, at high operational speeds, these systems would consider the conductors as discontinuities in the system that affect the operation and speed thereof
Many signal terminals or pins in these systems were connected to the same ground return conductor, and thus created a high signal to ground ratio, which did not lend themselves to high-speed signal transmission because large current loops are forced between the signals and the ground, which current loops reduce the bandwidth and increase the cross talk of the system, thereby possibly degrading the system performance.
Bandwidth (“BW”) is proportional to 1/√{square root over ((LC))}, where L is the inductance of the system components, C is the capacitance of the system components and BW is the bandwidth. The inductive and capacitive components of the signal delivery system work to reduce the bandwidth of the system, even in totally homogeneous systems without discontinuities. These inductive and capacitive components can be minimized by reducing the overall path length through the system, primarily through limiting the area of the current path through the system and reducing the total plate area of the system elements. However, as the transmission frequency increases, the reduction in size creates its own problem in that the effective physical length is reduced to rather small sizes. High frequencies in the 10 Ghz range and above render most of the calculated system path lengths unacceptable.
In addition to aggregate inductance and capacitance across the system being limiting performance factors, any non-homogeneous geometrical and/or material transitions create discontinuities. Using about 3.5 Ghz as a minimum cutoff frequency in a low voltage differential signal system operating at around 12.5 Gigabits per second (Gbps), the use of a dielectric with a dielectric constant of about 3.8 will yield a critical path length of about 0.25 inches, over which length discontinuities may be tolerated. This dimension renders impracticable the ability of one to construct a system that includes a source, transmission load and load within the given quarter-inch. It can thus be seen that the evolution of electronic transmission structures have progressed from uniform-structured pin arrangements to functionally dedicated pins arrangements to attempted unitary structured interfaces, yet the path length and other factors still limit these structures. With the aforementioned prior art structures, it was not feasible to carry high frequency signals due to the physical restraints of these systems and the short critical path lengths needed for such transmission.
In order to obtain an effective structure, one must maintain a constant and dedicated transmission line over the entire delivery path: from the source, through the interface and to the load. This would include the matable interconnects and printed circuit boards but it also includes bridging a transmission line over components as well as bridging a transmission line over a circuit board trace. This is very difficult to achieve when the delivery system is constructed from individual, conductive pins designed to interconnect with other individual conductive pins because of potential required changes in the size, shape and position of the pins/terminals with respect to each other. For example, in a right angle connector, the relationship between the rows of pins/terminals change in both the length and the electrical coupling. High speed interconnect design principles that include all areas between the source and load of the system including printed circuit boards, board connectors and cable assemblies are being used in transmission systems with sources of up to 2.5 Gbps. One such principle is the principle of ground by design, which provides added performance over a standard pin field in that coupling is enhanced between the signal and ground paths and single-ended operation is complimented. Another principle being used in such systems includes impedance tuning to minimize discontinuities. Yet another design principle is pinout optimization where signal and return paths are assigned to specific pins in the pin field to maximize the performance. These type of systems all are limited with respect to attaining the critical path lengths mentioned above.
The present invention is directed to an improved transmission or delivery system that overcomes the aforementioned disadvantages and which operates at higher speeds.